Mitogen-activated protein kinases (MAP) is a family of proline-directed serine/threonine kinases that activate their substrates by dual phosphorylation. The kinases are activated by a variety of signals including nutritional and osmotic stress, UV light, growth factors, endotoxin and inflammatory cytokines. One group of MAP kinases is the p38 kinase group that includes various isoforms (e.g., p38α, p39β, p38γ and p38δ). The p38 kinases are responsible for phosphorylating and activating transcription factors as well as other kinases, and are activated by physical and chemical stress, pro-inflammatory cytokines and bacterial lipopolysaccharide.
More importantly, the products of the p38 phosphorylation have been shown to mediate the production of inflammatory cytokines, including TNF and IL-1, and cyclooxygenase-2. Each of these cytokines has been implicated in numerous disease states and conditions. For example, TNF-α is a cytokine produced primarily by activated monocytes and macrophages. Its excessive or unregulated production has been implicated as playing a causative role in the pathogenesis of rheumatoid arthritis. More recently, inhibition of TNF production has been shown to have broad application in the treatment of inflammation, inflammatory bowel disease, multiple sclerosis and asthma.
TNF has also been implicated in viral infections, such as HIV, influenza virus, and herpes virus including herpes simplex virus type-1 (HSV-1), herpes simplex virus type-2 (HSV-2), cytomegalovirus (CMV), varicella-zoster virus (VZV), Epstein-Barr virus, human herpes virus-6 (HHV-6), human herpesvirus-7 (HHV-7), human herpesvirus-8 (HHV-8), pseudorabies and rhinotracheitis, among others.
Similarly, IL-1 is produced by activated monocytes and macrophages, and plays a role in many pathophysiological responses including rheumatoid arthritis, fever and reduction of bone resorption.
Additionally, the involvement of p38 has been implicated in stroke, Alzheimer's disease, osteoarthritis, lung injury, septic shock, angiogenesis, dermatitis, psoriasis and atopic dermatitis. J. Exp. Opin. Ther. Patents, 2000, 10(1).
The role of p38 MAP kinase as a therapeutic target in oncology has been reviewed: Podar, K. H.; Teru; Chauhan, Dharminder; Anderson, Kenneth C., “Targeting signalling pathways for the treatment of multiple myeloma”, Expert Opinion on therapeutic Targets 2005, 9, 359-381; Schultz, R. M., “Potential of p38 MAP kinase inhibitors in the treatment of cancer”, Progress in Drug Research 2003, 60, 59-92.
The inhibition of these cytokines by inhibition of the p38 kinase is of benefit in controlling, reducing and alleviating many of these disease states.
Many disease states are characterized by uncontrolled proliferation and differentiation of cells. These disease states encompass a variety of cell types and maladies such as cancer, atherosclerosis, and restenosis. In many such disease states kinases, important cellular enzymes that perform essential functions by regulating cell division and proliferation, appear to play a decisive role.
The molecular mechanisms and signaling pathways that regulate cell proliferation and survival are now receiving attention as potential targets for anticancer strategies. Recently, increased efforts have been directed at targeting the MAPK pathway, which integrates a wide array of proliferative signals initiated by receptor tyrosine kinases (RTKs) and G protein-coupled receptors.
The MAPK signal cascade includes the G protein Ras, which works at the upstream end of a core module consisting of 3 kinases: Raf, MEK1/2 and ERK1/2. Raf phosphorylates and activates MEK1/2, which in turn leads to the activation of ERK1/2. Raf kinase has long been considered an attractive target for drug discovery due to its importance as a potential checkpoint for cancer-related signal transduction (Strumberg and Seeber, Onkologie, 2005, 28: 101-107; Beeram et al., J. Clin. Oncol. 2005, 23: 6771-6790).
The importance of the MAPK signalling cascade for the proliferation and survival of tumor cells recently increased with the discovery of activating B-Raf mutations in human tumors. Activating Raf mutations have been identified in melanoma, thyroid, colon, and other cancers (Strumberg and Seeber, Onkologie, 2005, 28: 101-107; Bollag et al., Current Opinion in Investigational Drugs, 2003, 4:1436-1441). Thus, in addition to a role in controlling tumors with Ras mutations and activated growth factor receptors, inhibitors of Raf kinase may harbor therapeutic potential in tumors carrying a B-Raf oncogene (Sharma et al., Cancer Res. 2005, 65: 2412-2421).
The mammalian Raf serine/threonine kinase family consists of three 68- to 74-kd proteins termed A-Raf, B-Raf, and C-Raf (Raf-1), which share highly conserved amino-terminal regulatory regions and catalytic domains at the carboxyl terminus. Raf proteins are normally cytosolic but are recruited to the plasma membrane by the small G-protein Ras, which is an essential step for their activation by growth factors, cytokines, and hormones. At the membrane, Raf activation occurs through a highly complex process involving conformation changes, binding to other proteins, binding to lipids, and phosphorylation and dephosphorylation of some residues.
A variety of agents have been discovered that modulate Raf kinase, including antisense oligonucleotides and small molecules. These inhibitors prevent the expression of Raf protein, block Ras/Raf interaction, or obstruct its kinase activity. Down regulation of B-Raf activity by siRNA or through the kinase inhibitors leads to inhibition of the growth of melanoma cells and siRNA-mediated reduction of B-Raf led to decreased tumorigenic potential of 1205 Lu cells. Raf inhibitors currently undergoing clinical evaluation show promising signs of anti-cancer efficacy with a very tolerable safety profile.
Despite the progress that has been made, the search continues for low molecular weight compounds that are useful for treating a wide variety of tumors and other proliferative disorders including restenosis, angiogenesis, diabetic retinopathy, psoriasis, surgical adhesions, macular degeneration, and atherosclerosis. Thus, a strong need exists to provide compositions, pharmaceuticals and/or medicaments with anti-proliferative activity. Such compositions, pharmaceuticals and/or medicaments may possess not only strong activity, but also exert diminished side effects in comparison to other anti-proliferative agents. Furthermore, the spectrum of tumors responsive to treatment with such compositions, pharmaceuticals and/or medicaments may be broad. Active ingredients of this type may be suitable in the mentioned indication as single agent, and/or in combination therapy, be it in connection with other therapeutic agents, with radiation, with operative/surgical procedures, heat treatment or any other treatment known in the mentioned indications.